Hypotension and cardiac arrest have been observed in patients anesthetized with the anesthetics halothane, enflurane and thiopental. These anesthetics are in wide clinical use today. Preliminary evidence suggests that these anesthetics might decrease the availability of Ca2 ion required for cardiac contraction. This project is designed to study the effect of the above-mentioned anesthetics on structures in the myocardial cell that regulate Ca2 ion flux and control the intensity of contraction. The elements that will be studied are: the sarcolemma (SL), the outer membrane of the muscle cell; the sarcoplasmic reticulum (SR), a membranous network that controls the amount of myoplasmic Ca2 ion; and troponin (Tn), a protein that responds to Ca2 ion binding by changing its shape and initiating the contractile process. Present evidence suggests that the SR is affected by anesthetics but may not be the major site of alteration of contractility. The studies outlined will examine the interaction of halothane, enflurane and thiopental with the subcellular structures to observe alterations in Ca2 ion response. The results will quantify the relative effect of each anesthetic on each structure and a possible mechanism of action will be postulated. The data obtained will help in formulating pharmacologic interventions to prevent anesthetic-induced cardiac depression in the operating room.